The present invention relates to the development of oil fields and, more particularly, it relates to a method of oil production by thermal mining and can be used in the petroleum industry.
This invention can be used most efficiently in the development of oil fields characterized by the presence of highly viscous oils and fluid asphalts.
The present invention can also be used for developing oil deposits with depleted reservoir energy.
At present, such deposits cannot be developed efficiently by the conventional method wherein the production of oil is accomplished with the aid of wells drilled from the ground surface. The resulting recovery is rather low.
Known in the art for developing oil fields with highly viscous oils and fluid asphalts is a mining method of oil production without conveying oil-bearing rock to the earth's surface (cf., A.Ya.Krems et al., Shakhtnaiya razrabotka neftianykh mestorozhdenii--The Mining of Oil Deposits, Gostoptekhizdat Publishers, Moscow, 1955).
Said prior art method comprises driving a system of workings at a level of 10-30 m above the roof of the oil-bearing bed. Then, the mine field is divided into several areas in which fringe drifts are driven with drill chambers. From the drill chambers, inclined and straight wells are drilled into the oil-bearing bed according to some pre-selected system. The depth of the wells depends on the thickness of the oil-bearing bed.
The distance between the well faces, the number of wells and the system of driving the workings according to this latter oil production method may differ. The faces are arranged uniformly over the bed floor.
The well design provides for the use of a casing string lowered down to the roof of the oil-bearing bed, while the well face is open, i.e., uncased.
After drilling the wells, oil is recovered therefrom by the flowing method and then by air-lift. When employing the flowing method, oil is lifted through the wells to the drill chambers by reservoir pressure. In the case of air-lift, oil is delivered through the wells to the drill chambers owing to the injection of compressed air to the well face via additional pipes.
From the wells, oil is supplied to ditches provided in the workings. Together with water supplied to the ditches, oil is conveyed to units designed for the separation of oil from the bulk of water. From said units, oil is pumped to central underground oil collectors. Thereupon, following primary preparation and preheat, oil is fed to tanks located on the ground surface.
Said latter prior art method helps increase the recovery by a factor of three and above as compared with development by means of wells drilled from the earth's surface. However, the absolute value of recovery amounts to only about 6%.
Low recovery caused a need to employ mining methods of oil production, involving a physical effect upon an oil-bearing bed and the oil contained therein.
There is also known in the art a method of oil production by thermal mining, involving the exposure of the bed to the effect of steam and heat (cf., V.N. Mishakov et al., Opyt primeneiya teplovykh metodov pri shakhtnoi razrabotke mestorozhdenii vysokoviyazkikh neftei--On the Use of Thermal Methods upon Mining Highly Viscous Deposits, in Neftyanoe khzyaistvo--Journal of Petroleum Industry, No. 10, 1974, pp. 31-35).
Said prior art method provides for driving, above the oil-bearing bed, a plurality of underground workings including shafts, shaft workings, drifts and drill chambers.
Form the drill chambers located in the drifts, straight and inclined inlet and recovery wells are drilled. A heat carrier (steam) is delivered to the oil-bearing bed via inlet wells, which drives oil from the inlet wells to the recovery wells. From the face of the recovery wells, oil is air-lifted to the drill chambers.
Said method suffers from inadequate heating of the bottom portion of the bed and, as a result, a reduction of current production of oil, recovery and efficiency of the process of thermal mining of the oil-bearing bed.
According to another prior art method of mining an oil-bearing bed (U.S. Pat. No. 1,634,235), wells are drilled from underground workings located both above and below the oil-bearing bed. Steam treatment of face zones and extraction of oil therefrom is effected from shallow wells drilled from the workings from the top downwards or from the bottom upwards.
The face zone of the wells is heated by way of delivering steam to the well faces via pipes placed in the well while oil is extracted from the same wells.
The use of the latter prior art method in oil deposits with bottom water is disadvantageous in that the oil-bearing bed cannot be drilled from the bottom while the drilling of wells from the top involves a slow development of the oil-bearing bed. Sanding up occurs in the wells, air-lift of oil tends to be rather complicated, all this resulting in low recovery.
Still another prior art mining method of oil production (cf., U.S. Pat. No. 1,520,737) comprises driving a vertical shaft through an oil-bearing bed below which a drill chamber is arranged.
Inclined and ascending wells are drilled in a radial direction from the drill chamber. The method provides for alternate injection of a heat carrier into the oil-bearing bed through said wells and extraction of oil from the same wells following the heating of the oil-bearing bed in the region of the well face zone.
The method further provides for the delivery of a heat carrier (such as steam) via pipes passing through said wells for the purpose of cleaning the well face zone from oxidized oil and resinous substances, as well as for removing the well output. Oil extraction is effected by gravity flow.
The disadvantage of using said method in oil deposits with active bottom water resides in the difficulty of arranging a drill chamber below the oil-bearing bed and drilling rise wells. Under certain conditions, it becomes impossible to utilize said method.
Also known in the art is a method of mining oil deposits (cf., U.S.S.R. Inventor's Certificate No. 199,058), wherein a heat carrier is injected via pipes placed in level, flat-inclined or rise wells and provided near the face with a packer, while the extraction of oil is effected through perforated holes in the casing near the top of the well.
Said latter method suffers from a low rate of heating when used in oil deposits with bottom water.
There is further known a method of mining oil deposits, wherein a heat carrier is injected from workings located above a recovery gallery. The producing bed is heated by periodically injecting steam through a system of inlet wells. Without discontinuing the injection of steam, fluid such as oil and water is periodically extracted, followed by periodic injection of hot and then cold water, while continuing the extraction of fluid via wells of the recovery gallery.
This latter method suffers from slow heating of the bottom portion of the bed, especially so, in deposits with bottom water, and the resulting reduction of recovery and efficiency of the heat effect.
There is likewise known a prior art method of mining an oil deposit, which comprises injecting a heat carrier into the bed with the aid of inlet wells and extracting oil with the aid of recovery wells drilled from a single working gallery.
The latter prior art method suffers from a low rate of heating the bed due to the bottom water pressure when developing an oil deposit with underlying water.